1. Field of the Invention
The invention relates to a fuel injection device for an internal combustion engine, having at least two valve elements, each of which has a hydraulic control surface acting in the closing direction that is associated with a hydraulic control chamber, having a control valve that influences the pressure in the control chamber, and having loading devices that are able to act on the valve elements in the opening direction, in which the valve elements react at different hydraulic opening pressures prevailing in the control chamber, and to a method for operating a fuel injection device of this kind.
2. Description of the Prior Art
A fuel injection device of the type mentioned at the beginning is known from DE 101 22 241 A1, which discloses an injection nozzle for internal combustion engines having two valve elements situated coaxially relative to each other. Both of the valve elements are stroke-controlled, i.e. they open when the pressure of a hydraulic fluid in a control chamber is reduced. The force of the valve elements acting in the opening direction is generated by an injection pressure acting on a corresponding pressure surface. As a result, the outer valve element opens first, followed by the inner valve element. If only the outer valve element is to be opened, then the pressure reduction in the control chamber must be terminated promptly and the pressure must be increased again.
Fuel injection devices are provided with several valve elements for the following reasons:
In particular in diesel internal combustion engines, in order to reduce emissions and increase efficiency, it is necessary to inject the fuel in as finely atomized a form as possible into the corresponding combustion chambers of the engine. This can be achieved if the fuel travels into the fuel injection device at a high injection pressure.
Using several valve elements, each of which controls a certain number of fuel outlet openings, makes it possible, even if a small fuel quantity is to be injected, to achieve a sufficiently long injection duration with a good atomization quality without simultaneously having to accept an excessively long injection duration and/or an excessively high injection pressure if a large fuel quantity is to be injected.
The object of the present invention is to modify a fuel injection device of the type mentioned at the beginning so that it can be triggered in as simple a fashion as possible and nevertheless functions reliably. At the same time, its use should enable a good emissions and fuel consumption behavior of the associated internal combustion engine. A further object of the present invention is to provide a method of operation of a valve of the type mentioned at the beginning so that even if only one valve element is to be actuated, this occurs as needed in the fastest possible way.
The first object mentioned above is attained in a fuel injection device of this type in that the control valve is able to set at least three different pressure levels in the control chamber; all of the valve elements are closed at a comparatively high pressure level; one valve element is open at a medium pressure level; and all of the valve elements are open at a comparatively low pressure level.
The second object mentioned above is attained in a method of operation of the valve by virtue of the fact that in a fuel injection device of this type, in order to open only one valve element, the control chamber is first connected to a low-pressure connection and then, is simultaneously connected to the low-pressure connection and a high-pressure connection.